The proposed work aims to extend the high resolution of single neuron analysis with combined anatomical and immunocytochemical techniques for a more precise description of cellular, electrical membrane and ionic currents; neurotransmitter and neuromodulator action; and circuits of neuronal elements in the basal ganglia. Moreover, at the same time, the proposed work aims to provide a more meaningful interpretation of various nuclear functions of the basal ganglia than can be obtained by conventional single or multiple unit recording or by conventional anatomical technique. The areas of interest will be addressed with intensive usage of the well established methodology in our laboratory, whereby, intracellular recording and intracellular labeling with biocytin and other labeling materials are combined with subsequent light and electron microscopic analysis. In addition, histochemical methods, including retrograde and anterograde transport techniques, will be employed. This convergent multidisciplinary analysis will be directed to in vitro slice preparation and cultured and acutely dissociated neuron preparation obtained from rat neostriatum globus pallidus, entopeduncular nucleus, substantia nigra, and subthalamus to three sets of aims: The first set will characterize the membrane properties (including ionic conductances such as K, Na, Ca, etc.) of the neuron by the use of whole-cell (voltage) clamp technique in acutely dissociated or cultured neurons or by an intracellular current clamp recording in slice preparation. The second set will delineate the action of putative neurotransmitters or neuromodulators by monitoring changes in ionic conductances produced by the drugs or their agonists and antagonists. The transmitters to be studied are dopamine (DA), glutamate, and acetylcholine (ACh), which are the major known neurotransmitters and modulators involved in these nuclear operation. We will identify the transmitter and morphological phenotypes of the neurons under study by anatomical techniques by combined techniques of immunocytochemistry. The third set is to re-examine functional circuits involved among these nuclei (e.g., subthalamo-pallidal, striato-nigral, etc.) by trigger-averaging techniques with simultaneous recordings from the projection and its target neurons. Disequilibria of cholinergic, dopaminergic, glutaminergic, and GABAergic systems in the basal ganglia are believed involved in the pathophysiology of basal ganglia disease. The search for more specific treatments will be facilitated by a clearer understanding of the specific nature of the basal ganglia anatomy, physiology, pharmacology, and subsequent imbalance of extra-pyramidal operation.